Images of bottomside irregularities observed at topside altitudes

Abstract

We analyzed plasma and field measurements acquired by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during an eight-hour period on 13-14 January 2010 when strong to moderate 250 MHz scintillation activity was observed at nearby Scintillation Network Decision Aid (SCINDA) ground stations. C/NOFS consistently detected relatively small-scale density and electric field irregularities embedded within large-scale (∼100 km) structures at topside altitudes. Significant spectral power measured at the Fresnel (∼1 km) scale size suggests that C/NOFS was magnetically conjugate to bottomside irregularities similar to those directly responsible for the observed scintillations. Simultaneous ion drift and plasma density measurements indicate three distinct types of large-scale irregularities: (1) upward moving depletions, (2) downward moving depletions, and (3) upward moving density enhancements. The first type has the characteristics of equatorial plasma bubbles; the second and third do not. The data suggest that both downward moving depletions and upward moving density enhancements and the embedded small-scale irregularities may be regarded as Alfvénic images of bottomside irregularities. This interpretation is consistent with predictions of previously reported theoretical modeling and with satellite observations of upward-directed Poynting flux in the low-latitude ionosphere. Copyright 2012 by the American Geophysical Union.